The typical construction forms of vehicle body structures include the monocoque construction and the frame construction. The monocoque construction is a construction in which the conventional frame and body are integrally constructed from sheet steel, and is frequently used for passenger cars and the like. On the other hand, the frame construction is a construction in which the body is mounted on a tough framework called a frame. The frame construction is excellent in strength and is frequently used for trucks with a large loading capacity or with a large own weight, recreational vehicles receiving large input from road surfaces, e.g., during running on a rough road, and so on.
A truck has a large vehicle body and thus has a high bumper location. A recreational vehicle also has a rather high bumper location because the vehicle height is set high in order to avoid interference with road surfaces, e.g., on a rough road or because large-size wheels are adopted in order to improve the road ability on rough roads. For this reason, such vehicles are provided with an under protector attached at a position lower than the bumper location (e.g., cf. Japanese Patent Application Laid-Open No. 2003-72590).
When a frame vehicle with a high bumper location collides with a monocoque vehicle with a low bumper location, the above configuration results in making the under protector of the frame vehicle collide with the bumper of the monocoque vehicle to prevent the monocoque vehicle from slipping into the space under the floor of the frame vehicle (called an underride or the like) and to absorb the collision energy by effective deformation of the crushable zone of the monocoque vehicle.